#12 - On their way from their nest to a food source, ants of

[Administrator]

Complete Question Explanation

Must Be True. The correct answer choice is (C)

The author observes that most ants leave a trail of pheromones to guide themselves between a food source and their nest. However, at temperatures above 45 degrees Celsius, pheromones evaporate completely and are therefore useless. So if any Saharan ants are foraging for food in the afternoons when desert temperatures rise above 45 degrees Celsius, it is reasonable to suspect that these ants employ alternate means of navigation.

In fact-based stimuli such as this one, it is imperative to put the facts together and prephrase a logically valid conclusion before looking at the answer choices.

Answer choice (A): This inference would only be correct if we assumed that most ants live in the Sahara Desert, where the afternoon temperature is too high to allow them to use pheromones for navigation. However, since we have no reason to suspect that most ants are subjected to such high afternoon temperatures, this answer choice is no supported by the evidence presented in the stimulus.

Answer choice (B): While it is reasonable to conclude that most ants living in the Sahara Desert do not use pheromones for navigation, this is not the same as saying that most ants that do not use pheromones for navigation live in the Sahara Desert. It is entirely possible that many other places inhabited by ants have afternoon temperatures that rise above 45 degrees.

Answer choice (C): This is the correct answer choice. See discussion above. Also, notice how the carefully this answer choice qualifies the inference that some Saharan ants do not use pheromones for navigation. First, this statement is conditional, not absolute, thus avoiding the unwarranted assumption that any Saharan ants necessarily inhabit the Sahara Desert. If they do, however, and they forage for food only in the afternoon, the author properly concludes that they generally do not use pheromones for navigation since pheromones evaporate when temperatures rise above 45 degrees Celsius. The term "generally" further qualifies the language of this inference, which is appropriate since temperatures above 45 degrees Celsius are only typical (and not necessarily a de facto given) of afternoons in the Sahara Desert.

Answer choice (D): At first glance, this answer choice may seem attractive. After all, if ants cannot use pheromones for navigation, shouldn't they be using a different substance that does not evaporate in temperatures above 45 degrees Celsius? Perhaps. But not necessarily. The author never said that all ants must use some substance such as pheromones for navigation; she only observed that most ants do. It is perfectly possible that Saharan ants simply navigate by visual cues in place of pheromones.

Answer choice (E): This is a particularly tempting answer choice because it avoids making the otherwise unwarranted assumption that any Saharan ants actually forage for food in the afternoon. If they do, however, the author here concludes that they must be foraging for food less efficiently when temperatures rise above 45 degrees Celsius. There is some marginal support for that conclusion, particularly if we were to assume that (1) Saharan ants are like most other ants in that they use pheromones for navigation, and (2) that any other foraging method is by default less efficient than using pheromones.

Unfortunately, the stimulus offers no evidence to allow such assumptions. It is entirely possible that Saharan ants do not use pheromones at all, or if they do, that they can switch to an alternate means of navigation once the temperature gets too high. In addition, these alternate path-finding mechanisms may not be affected by higher temperatures at all, allowing ants to be just as efficient in climates where temperatures rise above 45 degrees Celsius.

It is important to remember that the correct answer choice in Must Be True questions must be capable of being completely proven by the stimulus. Even if an answer choice seems likely to be true, this is not good enough.

[avengingangel]

Do you mean that "ants living in the Sahara Desert" are different than "Saharan ants" ??? Thanks!


(For my own future reference: 3-120, #23)

[David Boyle]

Do you mean that "ants living in the Sahara Desert" are different than "Saharan ants" ??? Thanks!


(For my own future reference: 3-120, #23)

Hello avengingangel,

I'm not sure that that's what the Administrator is trying to say. "Saharan ants" may be a synonym for "ants in the Sahara", basically.

Hope this helps,
David

[PB410]

Is there anyone who can offer some direction in prephrasing MBT questions?
In the explanation above, the administrator mentions the importance of prephrasing inference questions. I came up with the correct answer, but it was only after going over each question and then checking them against the stimulus. I need to develop a way of approaching these questions more quickly. From the stimulus I was able to follow the information, but I wasn't sure where the answer choices would go in addressing the fact that pheromones evaporate when temperatures rise above 45 degrees.
Also do you have any advice on how to identify subtle wrong answer choices quickly? For example, choices A and E center on foraging for food, not on the path between nest and trail. Those subtleties are glaring without time constraints, but under pressure I struggle. Is it just a matter of closer reading?

Thanks!

[Francis O'Rourke]

Hi PB,

I'm going to quote some pieces of advice that have been posted elsewhere. Let me know if you still have questions about prephrasing Must be True questions after reading these:

From Prephrasing

For Must Be True questions, sometimes you'll be able to prephrase specifically and sometimes you won't. When you have conditional reasoning, you can often prephrase specifically by taking the contrapositive of the conditional statement or by linking multiple conditional statements together. When you don't have conditional reasoning, you may not be able to prephrase as specifically. Instead, make sure you understand each of the facts presented. Is there a pattern being presented over several facts? Is there a statement that is strangely worded or particularly tricky?

You won't always be able to come up with a specific prephrase because there are usually multiple things that Must Be True and you can't always anticipate exactly what they're going to give you in the answer choice. But if you know the facts well and have looked for any connections you can make between them or tricky points to focus on, you'll be in good shape going into the answer choices.

And using one specific example from viewtopic.php?t=6181

One you recognize that we are dealing with a Must Be True question that asks you essentially to come up with your own conclusion that makes sense in terms of the premises offered ("it would be reasonable to conclude that..."), you need to identify the premises and note any possible connections between the facts provided.

[lsatstudying11]

Hello,

In this case, do we know that most species of ants use the pheromone trails as guidance, or is that not something that is not necessarily supported? The question mentions that most ants use pheromones, and that these pheromones are used as guidance from nest to food. But, does that also mean that most ants use pheromones for this purpose of guidance? C seems to suggest that this is the case, but I am not sure. Thank you for your help!

[Mastering_LSAT]

Hello,

Could you please explain why C is the correct answer over E in more detail?

In MBT/MSS questions we cannot bring any outside information which is not mentioned in the stimulus. To assume that ants may use any alternate navigation methods is, as I see it, bringing an outside piece of information. To make things more confusing and pushing test takers from the correct answer choice C, the test-makers stated in C that “…ants generally do not use pheromones…” when the stimulus says explicitly that most ants use their pheromones and nothing in the stimulus is mentioned or implied about alternate navigation methods. Maybe ants in Sahara Desert when temperatures rise above 45 degrees Celsius still use pheromones, but do not rely on them as heavily? If the answer choice C stated that “…ants generally do not rely on pheromones…” that would make much more sense to me in picking the answer choice C over E.

My main concern is that by assuming or suspecting things like “ants may use another navigating system in Sahara Desert when temperatures rise above 45 degrees Celsius” or that “…ants do not use pheromones…” in Sahara Desert when temperatures rise above 45 degrees Celsius, we go beyond the scope of the stimulus.

Please help to clear my understanding as well as explain when we can make assumptions in MBT and MSS questions.

Many thanks!

[Robert Carroll]

Master,

Answer choice (C) does not claim that ants use any alternative means. It simply denies that they use pheromones in certain Saharan conditions. That might mean that such ants use nothing - they don't inhabit the Sahara, or any that do forage at other times than just the afternoon. So there is no objection to this answer based on "new information" about alternative means.

I think you are misinterpreting the first paragraph of our explanation as entailing that there ARE Saharan ants who forage only in the afternoon, and that, because pheromones are useless for them, they use some alternative means to forage. But that paragraph says "So if any Saharan ants are foraging for food in the afternoons when desert temperatures rise above 45 degrees Celsius, it is reasonable to suspect that these ants employ alternate means of navigation." That's a conditional! If nothing fulfills the sufficient condition, then nothing needs to fulfill the necessary. So if NO Saharan ants exist, the conditional is true, and we don't need any alternative means actually to exist.

This is actually a general feature of conditionals called "vacuous satisfaction." A conditional can be true when the sufficient condition is true of nothing - "All kings of France ruling in the 20th century had long beards" is true! Because there were no kings of France ruling in the 20th century, I can say anything I want about those non-existent people and still be making a true statement.

Applying the logic to answer choice (C), we can say "either no such ants exist, or if they do, they use alternative means to forage. So any of them (if they exist!) who are foraging are not using pheromones." It's true, and because it doesn't commit use to thinking any Saharan ants foraging only in the afternoon exist, it doesn't commit use to thinking that alternative means exist.

Robert Carroll

[ally.ni]

Hello,

I chose answer choice E for this one, and while I understand why answer choice C is correct, I am still unsure about how answer choice E is wrong based on the explanation. First, is Saharan ants not a subset of ants, which makes the stimulus valid for Saharan ants. And in addition aren't we assuming that there are other types of foraging methods that ants do not use in hot afternoons, which isn't supported by the stimulus?

Thanks!

[KelseyWoods]

Hi Ally!

You're correct that if the stimulus had told us that something was true of ALL ants, we would have been able to make an inference about any subspecies of ant, including Saharan ants. But take a look at that stimulus again. It tells us that "ants of most species leave a trail of chemicals called pheromones." Notice that this just refers to ants of most species, but does not say that this is true of all ants. As a specific species of ant, we don't know if Saharan ants are like ants of most other species or if they are one of the few species that does not leave a trail of pheromones.

And you're correct that the stimulus doesn't allow us to assume that there are definitely other types of foraging methods used by ants--but it also doesn't allow us to assume that there are not other types of foraging methods ants use. It's possible that pheromones are the only method of foraging available to ants. But it's also possible that they have other methods available to them as well. If the stimulus doesn't specifically rule out other foraging methods, we can't rule out other foraging methods either.

Hope this helps!

Best,
Kelsey